The invention relates to pneumatic tires having a reinforcement package under the tread area which improves the durability of the tire.
In the production of high-performance tires, i.e., tires that are designed to run at high speeds, overlay reinforcement has been shown to reduce radial runout of the tire and to stabilize the tire footprint at high speeds.
In U.S. Pat. No. 4,791,973, issued Dec. 20, 1988, a high performance tire having a chopped overlay is described. Said patent is hereby incorporated herein by reference. By chopped overlay, it is meant that the reinforcement cords in the overlay material are discontinuous, i.e., the reinforcement cords are separated by interruptions at random locations in the overlay material. The chopped overlay is said to provide the tire with high-speed endurance without adversely affecting the uniformity of the tire.
U.S. Pat. No. 2,945,525 describes an annular layer comprising ringed shaped reinforcing elements which have at least one interruption per each circumference of the tire. The layer described in the patent is a belt layer which is the sole reinforcement of the crown area of the tire.
U.S. Pat. No. 4,688,615, issued Aug. 25, 1987 teaches a tire with a reinforcement package wherein belt material is used to make a 0xc2x0 mid-ply belt, which is placed between conventional working belts in a tire. Said patent is hereby incorporated herein by reference. In the development of the mid-ply belt design, it was believed that placement of the mid-ply belt between belt reinforcement layers would provide durability and decrease interlaminar shear between the first and third belts. It was found that such a design concept can not be used in many tire designs, however, because the 0xc2x0 reinforcement in the mid-ply belt pulls down against the cords of the radially inward first belt when the tire is cured, causing the cords in the first belt and the mid-ply belt to contact each other.
In the conception of the present invention, the inventors conceived the idea of using the chopped overlay concept in the development of a mid-ply belt, believing that separations in the cord reinforcement in the mid-ply belt would prevent the pull down of the cords of a radially inward belt. In the particular tire constructed, it was also found that increasing the diameter of the green tire improved the cord spacing between the belts in the reinforcement package.
It is an object of the present invention to provide a pneumatic tire which has improved durability.
Other objects of the invention will be apparent from the following description and claims.
A pneumatic tire of the invention comprises at least two parallel annular beads (12), at least one carcass ply (14) wrapped around the beads, tread (16) disposed over the carcass plies in a crown area of the tire, sidewalls (18) disposed between the tread (16) and the beads (12), and a reinforcement package (15a-e) comprising a plurality of belts or breakers disposed between the tread (16) and carcass (14). The tire of the invention is characterized in that the reinforcement package (15a-e) has at least one lower belt (23,24,34,44,54) comprising continuous parallel reinforcement cords or filaments (27) disposed radially inward in the reinforcement package, at least one upper belt (21,22,32,42,52) comprising continuous parallel reinforcement cords or filaments (27) disposed radially outward in the reinforcement package, and at least one middle reinforcement ply (25,26,36,46,56) comprising discontinuous parallel reinforcement cords or filaments (28) disposed between the upper and lower belts. The discontinuous cords or filaments (28) are oriented substantially parallel to the centerline (31) of the reinforcement package (5a-e).
Several embodiments of the invention are disclosed. In a first embodiment, the reinforcement package comprises two upper belts (22), two lower belts (24) and one middle belt (26). In a second embodiment, the reinforcement package comprises one upper belt (21), one lower belt (23) and one middle belt (25). In other embodiments, the reinforcement package comprises two upper belts (32), one lower belt (34) and one middle belt (36); one upper belt (42), two lower belts (44) and one middle belt (46); and one upper belt (52), one lower belt (54) and two middle belts (56).
In each embodiment, the upper and lower belts have reinforcing cords (27) having alternating opposing angles of 15xc2x0 to 38xc2x0 with respect to the equatorial plane (EP), also known as the mid-circumferential or center-plane, of the tire.
In an illustrated embodiment, the reinforcing cords (27) in the upper and lower belts and reinforcing cords (28) in the mid-ply belt comprise polyethylene naphthalate.